Flask



FIG. 1 is a perspective view of the flask;

FIG. 2 is a front view thereof;

FIG. 3 is a top view thereof;

FIG. 4 is a bottom view thereof; and,

FIG. 5 is a perspective of the flask of FIG. 1 showing an unclaimed cup as an over cap.

The broken lines in the drawing views are for illustrative purposes only and form no part of the claimed design. 

The ornamental design for a flask, as shown and described. 